Generally, a reciprocating compressor can vary a compression capacity thereof by varying a voltage applied to a motor therein and thus by varying a compression ratio thereof.
The reciprocating compressor will be explained with reference to FIG. 1.
FIG. 1 is a block diagram showing a driving controlling apparatus for a reciprocating compressor in accordance with the prior art.
As shown in FIG. 1, the prior art reciprocating compressor is supplied with a voltage to control a stroke of a motor (not shown) therein by cutting off an input power (AC 220V) by controlling ON/OFF of a triac.
The motor inside the reciprocating compressor is wound by a coil with a uniform winding ratio. The reciprocating compressor is driven by the voltage to control the stroke.
The reciprocating compressor is supplied with a voltage to control the stroke by a switching operation of the triac. A mechanism for supplying the voltage to control the stroke generates noise, and thus an additional device for removing the noise is required.
To end this, a driving controlling apparatus for a reciprocating compressor capable of driving a motor by directly applying a commercial power to the reciprocating compressor has been proposed according to another embodiment of the prior art. In the driving controlling apparatus for a reciprocating compressor, a winding ratio of a coil of the motor of the reciprocating compressor is varied, and thus a capacitance is varied so as to enhance an efficiency of the reciprocating compressor.
A driving circuit of the reciprocating compressor according to another embodiment of the prior art will be explained with reference to FIG. 2.
FIG. 2 is a driving circuit of a reciprocating compressor according to another embodiment of the prior art.
A motor M inside the reciprocating compressor according to another embodiment of the present invention is provided with a main coil and a sub coil. A capacity of the motor is varied by selecting the main coil or both the main coil and the sub coil according to a load variation.
The selection of the coil will be explained. When a current load applied to the reciprocating compressor is larger than a reference load (over-load), a first relay (RY1) is switched so as to select only the main coil. As the result a constant of a counter electromotive force of the motor becomes small, a second relay (RY2) is closed, and a first capacitor (C1) and a second capacitor (C2) are connected in parallel with each other.
When a commercial power is applied to the reciprocating compressor, a current applied to the reciprocating compressor and a stroke of the motor inside the reciprocating compressor are increased. Accordingly, an output capacity of the reciprocating compressor is increased.
On the contrary, when a load applied to the reciprocating compressor is smaller than the reference load (low-load), the first relay (RY1) is switched so as to select both the main coil and the sub coil. As the result, the constant of the counter electromotive force of the motor becomes large, the second relay (RY2) is opened, and only the second capacitor (C2) is connected to the motor.
When a commercial power is applied to the reciprocating compressor, a current applied to the reciprocating compressor and a stroke of the motor inside the reciprocating compressor are decreased. Accordingly, an output capacity of the reciprocating compressor is decreased.
The number of windings (N) of the coil of the motor (M) inside the reciprocating compressor is proportional to the constant of the counter electromotive force of the motor (M), but is inversely-proportional to the stroke of the motor (M), which will be explained in the following formula 1.
                    Stroke        ≅                  Voltage                      Motor            ⁢                                                  ⁢            Constant                          ∝                  Voltage          N                                    [                  Formula          ⁢                                          ⁢          1                ]            
Herein, the number of windings N of the coil of the motor inside the reciprocating compressor is varied according to a load by a micro computer (not shown) so as to vary an output capacity of the reciprocating compressor.
When a commercial power is directly applied to the reciprocating compressor so as to drive the motor, the stroke of the motor inside the reciprocating compressor is drastically increased. In order to solve the problem, a PTC device was connected between the commercial power and the reciprocating compressor according to another embodiment of the prior art.